1. Technical Field
The present invention relates to an inkjet ink, an ink storage container, an inkjet recording apparatus, and recorded matter.
2. Background Art
In recent years, inkjet recording apparatuses have been widely used as image-forming apparatuses because the image-forming process is simple, full-color recording can be easily achieved, and high-resolution images can be obtained even with a simple structure.
Inkjet recording apparatuses are apparatuses for forming an image by ejecting an ink by using pressure generated by a bubble formed by heat, a piezoelectric effect, an electrostatic effect, or the like to allow the ejected ink to adhere to a recording medium. Inkjet recording apparatuses have been increasingly used as personal and industrial printers and in printing.
Pigment inks have recently been studied for in inkjet recording apparatuses.
Pigment inks have a problem in terms of insufficient storage stability.
JP-2006-342201-A discloses an inkjet ink containing water, a water-soluble organic solvent, a pigment, and a polymer dispersant for dispersing the pigment, the polymer dispersant having a weight-average molecular weight of 800 or more. In this inkjet ink, a characteristic value represented by (ratio of polymer dispersant to pigment in ink after centrifugal treatment for removing sediment (conditions for centrifugal treatment: centrifugal acceleration 9,000 g×30 min))/(ratio of polymer dispersant to pigment in ink before centrifugal treatment) is 1.0 to 1.5.
However, it is difficult to achieve both a high image density on plain paper and high storage stability.
JP-2011-122072-A neither exemplifies a copolymer obtained by using compounds represented by Formulae 5 to 8 in the present invention nor describes an effect of improving the image density on plain paper having a low content of a water-soluble polyvalent metal salt or an effect of improving dispersion stability of a pigment.
JP-2008-214530-A also neither exemplifies a copolymer obtained by using compounds represented by Formulae 5 to 8 in the present invention nor describes an effect of improving the image density.